Chip-based time-continuous monitoring of toxic effects on stem cell differentiation

Pesticides used to control unwanted insects are potentially toxic to humans. In assessing the risk involved in exposure to pesticides or complex chemical mixtures, an in vitro cell-based test can provide useful information regarding danger to human health. Cell differentiation is a biological process of fundamental importance in developing and adult organisms. In this paper, we propose a cell-based test system for continuous, label-free monitoring of the effect of test substances on stem cell differentiation. Using a prefabricated electrode-based chip and impedance measurement system, we investigated the influence of chlorpyrifos (a pesticide) on the differentiation of human mesenchymal stem cells (hMSCs) to adipocytes. The state of hMSCs on electrodes during adipogenic differentiation or after application of the cytotoxic substance was clearly reflected in the impedance measurement. Chlorpyrifos caused a partially uncovered electrode area with a decreased number of lipid vacuoles, thus leading to a rapid decrease in resistance in the cell layer. After removal of the chlorpyrifos, the cell layer resistance was regained due to the renewed covering of the electrodes by hMSCs. However, an increase in lipid vacuoles was not observed. From this, it was concluded that the measured resistance of hMSCs is determined by the electrical properties in the extra cellular space (e.g., cell/electrode or cell/cell gap), but not by the lipid vacuoles appearing in intracellular space during adipogenic differentiation.